The present invention relates to pumping molten metal and more particularly to an impeller shaft connection between a drive and an impeller in a molten metal pump.
Pumping molten metal is a difficult task and a challenge to designers of pumping equipment. The high temperature of molten materials (such as aluminum) and the corrosive effect of the molten material and components used in the refining or smelting processes prohibit the use of ordinary pumping equipment.
The pump drive motor, for example, should be situated above the molten metal level to isolate the components of the motor and drive assembly from the molten metal. Thus, an impeller shaft assembly is typically provided between the drive shaft and the impeller to transmit rotational forces from the driver or motor to the impeller.
It has been found that a graphite refractory, xe2x80x9cSilonxe2x80x9d(trademark), silicon carbide, and other heat resistant materials are suitable for impeller shafts due to the ability of these types of material compositions to withstand the heat and corrosive effects of molten metal.
FIGS. 1-3 are illustrative cross-sectional views of a shaft assembly A in which a shaft end B is received within a connector socket C. The socket C is typically connected to the drive shaft of a drive motor. Some prior devices transmit torsional forces from the type of socket C shown in FIGS. 1-3 and a shaft end B by providing a xe2x80x9cmodified squarexe2x80x9d coupling arrangement. The socket C includes a formed socket part D and the shaft end B includes a complimentary configuration E. The two shapes are closely fitted together.
On the other hand, if the two members are loosely interfitted as shown in exaggerated form in FIGS. 1-3, transmission of torsion from the socket member to the shaft is concentrated closer to the corners of the xe2x80x9cmodified squarexe2x80x9d configuration of the shaft end. This places the corner portions in shear and can cause fracture and premature wear.
It has thus remained desirable to obtain a fitting arrangement whereby an impeller shaft can be removed for replacement from an impeller and drive assembly, but in which transmission of torque, especially at the coupling area between the drive shaft and impeller shaft is transmitted without excessive shear forces being concentrated at corner sections of the formed impeller shaft end.